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Topic: Is it possible to clean ICs with Pure Alcohol ? (Read 3352 times) previous topic - next topic

jboyton

So you think the 99% concentration has a noticeably greater solvent power than the 91%? It would be interesting to see a blind test.

CrossRoads

I just know it took what seemed like 3 cleanings for the sticky feel to go away, and longer to dry.
Designing & building electrical circuits for over 25 years.  Screw Shield for Mega/Due/Uno,  Bobuino with ATMega1284P, & other '328P & '1284P creations & offerings at  my website.

polymorph

Quote
Here, in France, you can buy "Alcool à brûler" in any supermarket.  It consists of 90 to 95% ethanol with 5 to 10% methanol.  Both are highly volatile and leave no residue making it very good for cleaning.
equivalent here is rubbing alcohol.
Composition is different though its pretty good but im sure that there is something else in it , it feels slightly oily after evaporation

The french type cannot be imported to the uk without a licence, i tried once.
Incorrect. "Rubbing Alcohol" is isopropyl, water, and generally some kind of oil.

What he describes is called denatured alcohol in the USA. Ethanol with methanol and often a few other solvents. Works great as a degreaser, but attacks some plastics.

I generally use 99% isopropyl for cleaning electronics, but also use denatured alcohol for some tasks.
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polymorph

So you think the 99% concentration has a noticeably greater solvent power than the 91%? It would be interesting to see a blind test.

The key thing is that it leaves less water behind.
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jboyton

The key thing is that it leaves less water behind.
The solution doesn't evaporate?

polymorph

The alcohol evaporates quickly, the water not as quickly.
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jboyton

Not for a 91% solution. The vapor and liquid have the same composition. That's why it's impossible to obtain a higher concentration via simple distillation. I think that also means it is slightly more volatile than pure isopropanol. The 91% stuff should actually evaporate as fast or a little faster.

But maybe the higher concentration makes it a better solvent.

polymorph

Citation?

But... the 99% starts out with less water in it. So even if the alcohol evaporates more quickly, it reaches dynamic equilibrium at 91% and continues to evaporate at 91%, but it has reached that point more quickly.
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JoeN

#38
Sep 30, 2015, 02:54 am Last Edit: Sep 30, 2015, 02:58 am by JoeN
This is what I use.  Get it at Fry's or online, or seek a similar alternative.

I agree with Crossroads.  It usually takes 3 cleanings to get rosin flux "perfectly" cleaned off.  However, you don't need it perfect unless you are selling it or showing it to investors.  Once is pretty good.

I will never ask you to do anything that I wouldn't do myself.

jboyton

#39
Sep 30, 2015, 03:08 am Last Edit: Sep 30, 2015, 03:10 am by jboyton
Citation?

But... the 99% starts out with less water in it. So even if the alcohol evaporates more quickly, it reaches dynamic equilibrium at 91% and continues to evaporate at 91%, but it has reached that point more quickly.
I don't have a citation. And my chemistry is pretty poor.

This is from wikipedia:



The azeotrope is at a mole fraction of about 0.68. The molecular weights of isopropanol and water are 60.1 and 18.0 g/mol respectively. So the weight fraction of isopropanol at the azeotrope is approximately:

(0.68*60.1) / (0.68*60.1 + (1-0.68)*18.0) = 0.88

Converting that to volume is more complicated because there is contraction upon mixing. But if you ignore that you can get sort of close. The room temperature densities of isopropanol and water are 0.79 and 1.00g/cm3, so:

(0.88/0.79) /(0.88/0.79 + (1-0.88)/1.00) = 0.90

My seat of the pants calculation puts the azeotrope at 90% v/v. But that can't be right since the drug store sells isopropanol/water at 91%. The volume contraction or my inaccurate read of the chart in wikipedia have thrown off the value slightly.

I'm surprised it's so hard to find an online reference to the v/v percentage. But here's one.

You can't distill past the azeotrope using normal methods. But if you manage to get to a higher concentration by other means then the solution will have a vapor that is enriched in the less volatile component. That is, the water will vaporize faster than the alcohol in a 99% isoprop. soln.

But the azeotrope is a boiling point minimum; hence a vapor pressure maximum. So evaporation rate would be higher for the less concentrated stuff. I'm not convinced this matters that much. And eyewitness accounts of evaporation rate are subject to bias.


All that said, it could well be that pure isopropyl alcohol is superior to a 91% mixture, I really don't know. I wouldn't be surprised if some other solvent would be better overall for cleaning the gunk off of PCBs.


JoeN

#40
Sep 30, 2015, 03:21 am Last Edit: Sep 30, 2015, 03:23 am by JoeN
I wouldn't be surprised if some other solvent would be better overall for cleaning the gunk off of PCBs.
There are specific formulations for that.  At least the manufacturers think they are better.  They are certainly a bit more expensive than alcohol though.  OP could give this a try and get back to us.  Fry's sells it also.

http://www.all-spec.com/products/4140-1L.html

I will never ask you to do anything that I wouldn't do myself.

larryd

#41
Sep 30, 2015, 03:28 am Last Edit: Sep 30, 2015, 03:28 am by LarryD
The MSDS says:



They will be selling air next.

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jboyton

The composition of the 4140 flux remover varies by country. But ethanol seems to be the main ingredient. That's kind of interesting. I asked about that in another thread, whether ethanol had any advantages/disadvantages for cleaning as compared to IPA.

JoeN

Maybe I will pick up a bottle of it next time at Fry's and do a blind scrub-off test.  :)
I will never ask you to do anything that I wouldn't do myself.

dmjlambert

Everclear works best, and a big bottle of that goes a very long way for cleaning parts.   Works great, leaves no residue.   Not toxic unless you really drink more than a few swigs. 

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